5,699 research outputs found
Low Mass Stars and Brown Dwarfs around Sigma Orionis
We present optical spectroscopy of 71 photometric candidate low-mass members
of the cluster associated with Sigma Orionis. Thirty-five of these are found to
pass the lithium test and hence are confirmed as true cluster members, covering
a mass range of <0.055-0.3M_{sun}, assuming a mean cluster age of <5 Myr. We
find evidence for an age spread on the (I, I-J) colour magnitude diagram,
members appearing to lie in the range 1-7 Myr. There are, however, a
significant fraction of candidates that are non-members, including some
previously identified as members based on photometry alone. We see some
evidence that the ratio of spectroscopically confirmed members to photometric
candidates decreases with brightness and mass. This highlights the importance
of spectroscopy in determining the true initial mass-function.Comment: To appear in the 12th Cambridge Workshop on Cool Stars Stellar
Systems and the Su
Sparse Coding on Stereo Video for Object Detection
Deep Convolutional Neural Networks (DCNN) require millions of labeled
training examples for image classification and object detection tasks, which
restrict these models to domains where such datasets are available. In this
paper, we explore the use of unsupervised sparse coding applied to stereo-video
data to help alleviate the need for large amounts of labeled data. We show that
replacing a typical supervised convolutional layer with an unsupervised
sparse-coding layer within a DCNN allows for better performance on a car
detection task when only a limited number of labeled training examples is
available. Furthermore, the network that incorporates sparse coding allows for
more consistent performance over varying initializations and ordering of
training examples when compared to a fully supervised DCNN. Finally, we compare
activations between the unsupervised sparse-coding layer and the supervised
convolutional layer, and show that the sparse representation exhibits an
encoding that is depth selective, whereas encodings from the convolutional
layer do not exhibit such selectivity. These result indicates promise for using
unsupervised sparse-coding approaches in real-world computer vision tasks in
domains with limited labeled training data
Planet formation around stars of various masses: The snow line and the frequency of giant planets
We use a semi-analytic circumstellar disk model that considers movement of
the snow line through evolution of accretion and the central star to
investigate how gas giant frequency changes with stellar mass. The snow line
distance changes weakly with stellar mass; thus giant planets form over a wide
range of spectral types. The probability that a given star has at least one gas
giant increases linearly with stellar mass from 0.4 M_sun to 3 M_sun. Stars
more massive than 3 M_sun evolve quickly to the main-sequence, which pushes the
snow line to 10-15 AU before protoplanets form and limits the range of disk
masses that form giant planet cores. If the frequency of gas giants around
solar-mass stars is 6%, we predict occurrence rates of 1% for 0.4 M_sun stars
and 10% for 1.5 M_sun stars. This result is largely insensitive to our assumed
model parameters. Finally, the movement of the snow line as stars >2.5 M_sun
move to the main-sequence may allow the ocean planets suggested by Leger et.
al. to form without migration.Comment: Accepted to ApJ. 12 pages of emulateap
The discovery of a low mass, pre-main-sequence stellar association around gamma Velorum
We report the serendipitous discovery of a population of low mass, pre-main
sequence stars (PMS) in the direction of the Wolf-Rayet/O-star binary system
gamma^{2} Vel and the Vela OB2 association. We argue that gamma^{2} Vel and the
low mass stars are truly associated, are approximately coeval and that both are
at distances between 360-490 pc, disagreeing at the 2 sigma level with the
recent Hipparcos parallax of gamma^{2} Vel, but consistent with older distance
estimates. Our results clearly have implications for the physical parameters of
the gamma^{2} Vel system, but also offer an exciting opportunity to investigate
the influence of high mass stars on the mass function and circumstellar disc
lifetimes of their lower mass PMS siblings.Comment: Monthly Notices of the Royal Astronomical Society, Letters - in pres
Sidestepping Copyright: British Fairy Tale Anthologies of the 19th Century
One question is how in the golden period of fairy tale anthologising the work of the anthologists escaped the complete influence of copyright law with its paradigm of the individually authored work. The answer, it is suggested, lies, in part, in the early anthologists who formed a folklore society, saw themselves as anthropologists of folk culture, and treated copyright as largely irrelevant for the sake of their perception of the common good, and, in part, in the structure of copyright law itself which does not mandate but simply permits proprietary rights to be asserted
Light-activated resistance switching in SiOx RRAM devices
We report a study of light-activated resistance switching in silicon oxide (SiOx) resistive random
access memory (RRAM) devices. Our devices had an indium tin oxide/SiOx/p-Si Metal/Oxide/
Semiconductor structure, with resistance switching taking place in a 35 nm thick SiOx layer. The
optical activity of the devices was investigated by characterising them in a range of voltage and
light conditions. Devices respond to illumination at wavelengths in the range of 410–650 nm but
are unresponsive at 1152 nm, suggesting that photons are absorbed by the bottom p-type silicon
electrode and that generation of free carriers underpins optical activity. Applied light causes charging
of devices in the high resistance state (HRS), photocurrent in the low resistance state (LRS),
and lowering of the set voltage (required to go from the HRS to LRS) and can be used in conjunction
with a voltage bias to trigger switching from the HRS to the LRS. We demonstrate negative
correlation between set voltage and applied laser power using a 632.8 nm laser source. We propose
that, under illumination, increased electron injection and hence a higher rate of creation of Frenkel
pairs in the oxide—precursors for the formation of conductive oxygen vacancy filaments—reduce
switching voltages. Our results open up the possibility of light-triggered RRAM devices
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